If you are taking a feed from the PA, then the likelihood is that the sound won't be great as the vocals are likely to be too loud - and it will sound very dry.
To get around this, and you have a desk that support this, you can set up a matrix mix. You can have some ambient mics to bleed in a bit of the venue sound to make it sound more realistic.
Otherwise, a descent stereo condenser independent of your desk may give you acceptable results. I'm typing all this being mindful that you have to set everything up... so you may find that taking the audio from one of the zoom cameras may be a quick and easy fix. Having done a number of live streams with bands, do not brush over the mixing part. The audio has to be good - better than the video - to hold people's attention. People will not tolerate poor audio - but they are more forgiving when it comes to video. But getting video right is the cherry on top. Remember to offset your audio in OBS if needs be to get good sync between audio and video.
In your setup, the easiest way is probably to position the camera suitably far enough from the stage to get good audio and a wide shot of the stage... and use that audio from that zoom - and just that audio - so as your scenes in OBS change, the cameras do and the audio doesn't.
If you want to stream to multiple platforms, not have any "free tier" branding on restreamed feeds, you may wish to build a raspberry pi to take care of that -
You can get away with using a phone network if you signal is bang on (and use a wired connection to your phone when hotspotting) - but there is risk of degradation. Remember, people go live with their phones all the time on streaming platforms - but if there are any low spots or loss of signal (worst case), be prepared for dropped frames, lower resolutions etc. Wifi is better... Wired is best. Work with what's available to you Beggars can't be choosers.
Above all, don't let it take your focus away from your live performance!
The biggest thing however - is lighting. Don't expect miracles out of an 8bit video source - especially in low light. Some white LED panels to help the cameras out. And remember that native HDMI has a finite transmission length.